Study On Dynamics Behaviors And Gas Releasing Characteristics Of Gas-bearing Coal Under Dynamic Load

As coal mining enters into deep mining stage,the mining depth will continue to increase.Correspondingly,the stress,gas pressure and gas content will increase gradually.And the structure of mining field becomes more and more complex,which induces that the coupling disasters of stress and gas will be serious and complex.In addition,the complex dynamic disasters occur frequently.For example,coal outburst or strong earthquake causes abnormal gas emission and dynamic load induces coal and gas outburst.Nowdays,the coal and rock failures under impact load are mainly researched.However,there are short of studies aiming at the dynamics of gas-bearing coal and gas releasing under impact load.In this dissertation,by means of the experiments in laboratory,theory analysis and numerical simulation,the dynamics behaviors of gas-bearing coal and gas releasing under dynamic load(shock load: no fracture;and impact load: failure)will be researched systematically.The dynamics constitutive equation of gas-bearing coal and gas migration equations under dynamic load are established.Then the multifield coupling model of gas-bearing coal is proposed.Further,the coupling evolution mechanisms of stress field,damage field and gas field of gas-bearing coal during impact failure will be revealed.The main conclusions are as follows:The split Hopkinson pressure bar(SHPB)experimental system of gas-bearing coal was built,and the function of impact dynamics experiments of gas-bearing coal could be achieved on SHPB.And the relationships between dynamics behaviors of gas-bearing coal and axial load,confining pressure,gas pressure and shock load/impact load were analyzed.The results showed that confining pressure and dynamic load are helpful for improving the dynamic compressive strength and deformation resistance of gas-bearing coal.The adsorption swelling,expanding effects and corrosion effects of gas to coal will weaken its ability to resist external load.Under shock load,axial static load performs to improve the compressive strength and resistance to deformation of gas-bearing coal,and under impact load,axial static load seems to weaken the coal strength and degrades the deformation ability.The strain rate effects of gas-bearing coal under the combined loading of axial load,confining pressure,gas pressure and shock load / impact load were studied.The laws of dynamic compressive strength,peak strain / failure strain with strain rate wereanalyzed.The universality of strain rate in coal and rock field was demonstrated.The results showed that below critical strain rate,the dynamic compressive strength,peak strain / failure strain increase with strain rate,while beyond critical strain rate,the previous index value will be stable.The gas releasing characteristics of gas-bearing coal under shock load and impact load were researched,and the evolution laws of gas releasing with time were analyzed under the conditions of different axial static load,confining pressure,gas pressure and dynamic load.And the maximum gas releasing velocity and instant permeability changes with previous four factors were determined.Then the gas abnormal emission mechanisms of gas-bearing coal induced by dynamic load was revealed.Based on viscoelastic theory,Terzaghi effective stress principle and the statistical damage theory,the dynamics constitutive equation of gas-bearing coal was deduced in details,with considering the axial static load,confining pressure and gas pressure and the dynamic load factors.Combined with the gas adsorption equilibrium equation,diffusion equation and gas seepage equation,the gas transport equations of gas-bearing coal under dynamic load were established.Through porosity and gas releasing rate,the link between dynamics constitutive equation and gas migration equations under dynamic load was created.Then the multifield coupling model of gas-bearing coal under dynamic load was established,and the multifield coupling mechanisms of gas-bearing coal were revealed.Eventually,this model was verified by numerical simulation from sample scale.In terms of geological conditions about 4112 tunneling face in + 100 east-first mining area,some mine,the proposed multifield coupling model of gas-bearing coal under dynamic load was applied to explain the coupling process of stress and gas during coal and gas outburst.Then the features and causes of major coal and gas outburst were analyzed.The results showed that the complicated geological structure and stress environment is the prerequisite of this accident,the dynamic load within huge energy produced by fault slipping induced by mining activities is the direct cause of this disaster,and vast gas desorption caused by dynamic load is the main reason of abnormal gas emission during this coal and gas outburst.The research results in this dissertation are of theoretical significance for improving impact dynamics of gas-bearing coal and revealing the mechanisms of complex disasters of gas-bearing coal,and also of application value for promotingthe prevention and control of dynamic disasters of gas-bearing coal.